Mechanical motor encoders are well known in the art, and come in many varieties. A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. They are therefore used to determine the amount of rotation of a shaft in a rotating machine.
In 2D and 3D scanners, such as optical scanners and x-ray machines, one or more sensors and/or radiation sources typically move or rotate around the object being imaged. For example, in a Cone Beam Computed Tomography (CBCT) scanner, an x-ray source and x-ray sensor are mounted on a ring, which rotates around a person being scanned. When reconstructing the volumetric 3D x-ray image, it is important to know the geometry of the scanner with respect to the patient. For this reason, the patient is typically fixated using a head band to keep the patient from moving during an exposure, and rotary encoders are typically used to determine the position of the x-ray source and sensor relative to the patient.
U.S. Pat. No. 6,079,876 discloses an X-ray system having a position indicator arranged separate from the X-ray apparatus onto which a camera is directed for determining the positions of the X-ray source and the X-ray receiver.
U.S. Pat. No. 6,050,724 discloses a method of position detection in X-ray imaging, wherein the detector device is mounted on the X-ray apparatus and the indicator device is provided so as to be stationary on the object to be examined.
U.S. Pat. No. 6,379,041 discloses an X-ray apparatus with an arrangement for determining intrinsic imaging parameters including X-ray-positive marks which are allocated to the X-ray source and which are in the path of an X-ray beam emanating from the X-ray source, these marks following displacement of the X-ray system.
However, it remains to disclose a cone beam computed tomography system wherein physical motor encoders are not needed to determine the movement of the source and sensor in a scanning system.